We have prepared genomic and cDNA clones including MHC gene products expressed in B cells, T cells and teratocarcinoma cells. We will extend these genomic clones with the ultimate goal of obtaining the entire chromosomal region embedding the MHC complex in overlapping genomic clones. We will characterize the DNA controlling the expression of gene products in different types of cells or cells at different stages of differentiation. We have constructed a range of recombinant HLA-B7 clones and are studying their expression in injected mouse embryos. We have also isolated class II and class III clones.